A fluid dynamic bearing device is a bearing device including a stator and a rotor, which holds the stator and the rotor in a non-contact manner through a pressure generated by a dynamic pressure action, which is generated in a fluid (for example, lubricating oil) filled into a bearing gap between the stator and the rotor. The fluid dynamic bearing device has features such as high-speed rotation, high rotational accuracy, and quietness. In recent years, by taking advantage of those features, the fluid dynamic bearing device has been suitably used as a bearing device for a motor to be mounted to various electrical apparatuses such as information apparatuses. Specifically, the fluid dynamic bearing device has been suitably used as a bearing device to be incorporated into, for example, a spindle motor to be mounted to a disk drive such as an HDD, a polygon scanner motor to be mounted to a laser beam printer, and a fan motor to be mounted to a PC.
Of the above-mentioned motors, for example, in the spindle motor for a disk drive, the fluid dynamic bearing device incorporated thereto includes a radial bearing portion for supporting the rotor in a radial direction, and a thrust bearing portion for supporting the rotor in a thrust direction. In recent years, both the radial bearing portion and the thrust bearing portion have been constructed of fluid dynamic bearings in many cases, which are provided with dynamic pressure generating portions, such as dynamic pressure generating grooves, each arranged in any one of the two surfaces opposing through a radial bearing gap and a thrust bearing gap.
Nowadays, the price of the information apparatuses has been rapidly dropped and the use of mobile information apparatuses has been rapidly spread, which severely raises a demand for reduction in cost and weight of the fluid dynamic bearing device. In order to meet the demand, there have been various proposals to partially or entirely form the stator and the rotor of a resin, and as an example thereof, there is a fluid dynamic bearing device disclosed in JP 2005-282779A (Patent Document 1). In the fluid dynamic bearing device disclosed in Patent Document 1, the housing serving as the stator is injection-molded into a bottomed-cylindrical shape using a resin material, and the thrust bearing portion constructed of the fluid dynamic bearing is formed between the housing and the shaft member serving as the rotor, which is arranged on the inner periphery of the housing. In the fluid dynamic bearing device, at the time of activation, stop, or the like, sliding contact occurs between the end surface (inner bottom surface) of the housing and the opposing end surface of the shaft member. In order to prevent the end surface of the housing from being worn out by the sliding contact, the resin material that forms the housing is generally formulated with a predetermined amount of reinforcing fiber.
However, depending on the fiber diameter or the like of the reinforcing fiber to be formulated into the resin material, the counterpart member may be damaged and worn out . Therefore, there is a proposal in which the fiber diameter or the like of the reinforcing fiber to be formulated is specified (see, for example, Patent Document 2). In the fluid dynamic bearing device disclosed in Patent Document 2, the fiber diameter of the reinforcing fiber to be formulated is limited to 1 to 12 μm, to thereby prevent the above-mentioned trouble.